Thermosensitive recording materials utilizing a color-developing reaction between a leuco dye and developer have been used not only as recording materials, such as papers for facsimile, cash registers, and various printers, but also in a wide variety of fields because such thermosensitive recording materials are relatively inexpensive, recording devices thereof are small in size, and maintenance of the recording devices is relatively easy.
As the fields of applications expand and as the recording devices have been diversified and achieved high performance, use environment and storage environment of recording materials have become increasingly severe, and thus more superior characteristics as well as excellent sensitivity and image quality of recorded image have been desired.
To date, as a technique to avoid decoloration of developed color image due to oils or plasticizers, a thermosensitive recording material containing a particular diphenyl sulfone-crosslinked compound as a developer (see Patent Document 1) has been proposed. Furthermore, for labels used for food products or test tubes in hospitals, since such labels may be brought into contact with alcohol having a high concentration, a thermosensitive recording material containing a particular urea urethane compound (see Patent Document 2) has been proposed to avoid decoloration due to such contact. However, these thermosensitive recording materials have problems of causing discoloration in the blank paper when stored for a long period of time (background fogging) although these thermosensitive recording materials can achieve high quality regarding preservability of its recorded part.
Furthermore, to suppress change of hue in the blank paper when the paper is stored for a long period of time, a thermosensitive recording material containing a diacetone-modified polyvinyl alcohol in an adhesive agent in a protective layer and a hydrazine-based compound in a thermosensitive recording layer (see Patent Document 3), and a thermosensitive recording material containing diacetone-modified polyvinyl alcohol and acrylic resin in an adhesive agent in a protective layer and a hydrazide compound in a protective layer (see Patent Document 4) have been proposed. However, to date, these thermosensitive recording materials are not always satisfactory regarding lowering of brightness although these thermosensitive recording materials are effective regarding yellowing of the blank paper.
Furthermore, as a technique to enhance water blocking properties, thermosensitive recording materials that use acetoacetyl-modified polyvinyl alcohol in a thermosensitive recording layer, that contain a (meth)acrylamide copolymer having a core-shell structure as a water dispersible resin in a protective layer, and that contain a crosslinking agent at least in the protective layer (see Patent Documents 5 and 6) have been proposed. Furthermore, a thermosensitive recording material containing a polyamide resin and a polycarboxylic acid dihydrazide compound in a thermosensitive recording layer and containing, as a water-based adhesive agent in a protective layer, at least one type selected from the group consisting of acetoacetyl-modified polyvinyl alcohol and diacetone-modified polyvinyl alcohol (see Patent Document 7) has been proposed. However, these thermosensitive recording materials cannot exhibit sufficient water blocking properties and have problems of worsening lowering of recording sensitivity and worsening yellowing of the blank paper when the amount of the crosslinking agent is increased to further enhance the water blocking properties.
Furthermore, as a technique to achieve higher image preservability, thermosensitive recording materials containing a particular diphenyl sulfone-crosslinked compound as a developer (see Patent Documents 1 and 8) have been proposed. However, these thermosensitive recording materials have problems of causing discoloration in the blank paper when stored for a long period of time (background fogging) although these thermosensitive recording materials can achieve high quality regarding preservability of its recorded part. Although the background fogging can be improved by using a color developer having a high melting point, the recording sensitivity is lowered thereby, and it is not possible to satisfy all the qualities.
Furthermore, since thermosensitive recording materials utilize a mechanism which develops color by melting a leuco dye and a color developer using heat and bringing them into contact, sticking, by which a component of a thermosensitive recording material melted using the heat attaches to a recording head and then the melt-attached part is forcibly peeled off by a feed roll, and sticking of dirt to a thermal head are easily caused.
To improve so-called head matching properties, including sticking and sticking of dirt to a thermal head, a technique of blending stearic acid amide and zinc stearate at a weight ratio in the range of 3:1 to 1:3 in a thermosensitive recording layer (see Patent Document 9), and a technique of blending higher fatty acid together with a metal salt of higher fatty acid in a thermosensitive recording layer (see Patent Document 10) have been also proposed. However, further improvements have been demanded to achieve reduction in power consumption of printers, lowering torque of paper feeders, and processing at a higher speed, for low-voltage printers such as mobile printers.